Potentiometer electrical resistance elements of palladium base alloys



United States Patent 2,890,114 POTENTIONIETER ELECTRICAL RESISTANCE ELEMENTS 0F PALLADIUM BASE ALLOYS Konrad Ruthardt and Hermann Speidel, Hanan (Main), Germany, assignors to W. C. Heraeus G.m.b.H., Hanan (Main), Germany, a German body corporate No Drawing. Application August 18, 1953 Serial No. 375,051 Claims priority, application Germany August 19, 1952 6 Claims. (Cl. 75-172) The most diverse and mutually incompatible demands are imposed on resistance materials for potentiometers and similar electrical devices in which the wiper eifects travel over and rubbing contact with the contact surfaces. Similarly potentiometer materials should exhibit only small variation with temperature and time and have a high specific resistance. Furthermore, they should be easily formable during manufacture but possess also a high accuracy and resistance to mechanical friction and pressure as well as a high stability to atmospheric and chemical influences. More particularly the highest demands are imposed upon them even under unfavourable atmospheric conditions as are very often manifested in the chemical industry so that safe and exact operation of electrical control members provided with the potentiometers may be ensured. For example, the resistance can exhibit serious faults and become useless if the contact resistance between the wiper member and the potentiometer winding increases with time due to oxidation.

Previously it has been proposed to use mainly platinum and gold alloys owing to the most varied requirements imposed upon the materials. Therefore, alloys of platinum with copper or nickel have been known for these indicated properties, whcih alloys are characterised by a great constancy in the value of the resistance, and chemical and mechanical stability. Furthermore, there have been proposed alloys of gold with the most varied base metals, such as iron, manganese, nickel and vanadium, whereby very good workability and especially high specific resistance have been obtainable. Further, palladium-silver alloys with base metals, such as tungsten and molybdenum or alloys of these two metals together have also been used for potentiometers. However, this has always signified comparatively complicated alloys having a large number of components the control of which is not simple.

It has now been shown that a simple alloy of palladium with the metals tungsten or molybdenum singly or together possess advantageous electrical, mechanical and chemical properties which make them exceptionally suitable for potentiometer resistances of high value. According to the invention the metals tungsten or molybdenum or both metals in quantities from 1 to 30%, particularly to 25%, are alloyed with palladium.

Quite apart from the fact that the materials for potentiometers according to the invention exhibit a lower specific weight and a much lower price compared with the known gold and platinum alloys as a result of the vuse of palladium, what is technically and scientifically more important is the outstanding merit that the proposed palladium alloys with tungsten or molybdenum allow very high specific electrical resistance to be obtained as a binary alloy, without the other properties of stability, fuseability, formability and constancy of re sistance suffering thereby. A higher specific resistance is important for potentiometer alloys, as is well-known, in order to be able to deal easily with large voltages.

Whilst it was generally not possible with platinum alloys to attain specific resistances in the range of 1 ohm per square mm. per metre, at least when the remaining requirements for potentiometer materials had to be fulfilled, this could be obtained with gold as the basic material but only by additive alloying of metals such as vanadium, molybdenum and tantalum or with multi-element alloys of gold with vanadium, iron and manganese. It is not even possible to attain the desired values of specific resistance with the known palladium-silver alloys or with tungsten and molybdenum or alloys of the two metals together. In contradistinction, the new palladium alloys fulfil these requirements in the most favourable manner. As an indication of the high specific electrical resistance obtainable, the specific resistance values for the following combinations are set forth:

The advantage of the new alloys compared with gold alloys, particularly with vanadium, apart from their high specific resistance, consists in their favourable mechanical properties and high stability. They may be easily melted and render possible a simplified heat treatment. The potentiometers made from these alloys have a bright surface Without a marked transition resistance on account of their high resistance to oxidisation.

We claim:

1. A potentiometer electrical resistance element in wire configuration being composed of a palladium alloy consisting of 1% to 30% of a. metal selected from the group consisting of tungsten, molybdenum, and mixtures thereof, the balance of said alloy being palladium.

2. A potentiometer electrical resistance element in Wire configuration composed of a palladium alloy consisting of 5% to 25% of a metal selected from the group consisting of tungsten, molybdenum, and mixtures thereof, the balance of said alloy being palladium.

3. A potentiometer electrical resistance element in wire configuration composed of a palladium alloy consisting of 5% to 25% of tungsten, the balance of said alloy being palladium.

4. A potentiometer electrical resistance element in wire configuration composed of a palladium alloy consisting of 5% to 25 of molybdenum, the balance of said alloy being palladium.

5. A potentiometer electrical resistance element in wire configuration composed of a palladium alloy consisting of 5% to 25% of a mixture of tungsten and molybdenum, the balance of said alloy being palladium.

6. A potentiometer electrical resistance element in 5 Wire configuration composed of a palladium alloy consiSting of 7% to 20% of molybdenum, the balance of said alloy being palladium.

References Cited in the file of this patent UNITED STATES PATENTS 1,779,603 Kingsbury Oct. 28, 1930 2,537,733 Brenner Jan. 9, 1951 FOREIGN PATENTS 394,045 Germany Apr. 12, 1924 621,152 Germany Nov. 2, 1935 OTHER REFERENCES Metals Handbook (1948 ed.), publ. by ASM; pages 1122 and 1126 relied on.

Gmelins Handbuch der anorganischen Chemie, Tell 68, Platin A5, 1949; page 597 relied on. 

1. A POTENTIOMETER ELECTRICAL RESISTANCE ELEMENT IN WIRE CONFIGURATION BEING COMPOSED OF A PALLADIUM ALLOY CONSISTING OF 1% TO 30% OF A METAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, MOLYBDENUM, AND MIXTURES THEREOF, THE BALANCE OF SAID ALLOY BEING PALLADIUM. 